As a core component for data transmission, the wavelength division multiplexer/demultiplexer (WDM) is extensively utilized in on-chip optical interconnect networks, where the most crucial parameters for these devices include device size, insertion loss, and crosstalk levels. To address the issues of large size and uneven optical power distribution in conventional silicon-based arrayed waveguide gratings (AWGs), a 1×4 WDM based on a silicon-on-insulator (SOI) platform incorporating a ring reflector-assisted multimode interference waveguide is proposed, which can realize the wavelength separation of different channels. The core size of the device is only 10 μm×34 μm, and the minimum crosstalk between adjacent channels is -14.42 dB.